This invention pertains to improvements in apparatuses for sharpening the teeth of circular saws, and particularly to an apparatus that improves the overall effectiveness of a commonly used sharpening device that utilizes stationary wear plates.
Circular saw blades having replaceable teeth are as commonly used today in modern sawmills as they have been for many years in the commercial lumber industry. These saws come in varying sizes and require frequent maintenance in order to keep them effectively sharp and productive. Over the years, many devices have been used to sharpen the teeth of the saws. The most popular saw grinders typically employ a power-driven rotary grinding wheel mounted on a grinder carriage. Such devices are well known in the art; however, there have been no significant advances therein for some time. U.S. Pat. Nos. 2,249,743, 2,439,279, 2,651,219, 3,880,019, and 4,711,142 each relate to hand-held, motor driven saw blade sharpeners. Of these devices, only the grinder disclosed in U.S. Pat. No. 2,249,743 and the improvements thereto are readily available and commonly used in the industry today. The most popular of these improvements is a saw sharpener referred to as the “Jockey Grinder,” produced by Hanchett Manufacturing in Big Rapids, Mich.
In general, as shown in FIGS. 1 and 2, a conventional saw grinder 10 includes a two-piece carriage 12, formed of a front panel 17 and a back panel 19. The back panel 19 is shown partially in phantom in FIG. 2. Front panel 17 and back panel 19 are bolted together by threaded fasteners 18, thereby capturing therebetween and supporting a handle 14 and a dividing block 16. The handle 14 connects to an adjustable mounting bracket 20 for mounting a motor to drive power-driven grinding wheel 24, shown in FIGS. 1 and 2 as an electric drill 22. A conventional front wear plate 30 is attached to the underside of the dividing block 16 using threaded fasteners passing through recessed aperture 37 (FIGS. 3a and 3b) into a corresponding hole (not shown) machined in the underside of the dividing block 16. Similarly, a conventional back wear plate 32 is attached to the underside of the handle 14 using threaded fasteners passing through recessed apertures 52 (FIGS. 4a and 4b) into corresponding holes (not shown) in the underside of the handle 14.
When in use, the entire weight of the saw grinder 10 rests on the stationary wear plates 30, 32 on the peripheral edge of the circular saw blade 28 consisting mainly of a plurality of replaceable teeth 26. The process of grinding the teeth 26 is initiated when the operator, or sawyer, positions the grinding wheel 24 under the tooth 26 by lifting the handle 14 and maneuvering the saw grinder 10 into an arcuate slot referred to as the gullet 33. The sawyer then sets the saw grinder 10 in the starting position shown in FIGS. 1 and 2, with the front and back wear plates 30, 32 now in contact with the peripheral edge of the saw blade 28. Using the handle 14 again, the sawyer eases the saw grinder 10 in the backward direction shown by arrow 36 to engage the bottom cutting edge of the tooth 26. The sawyer then moves the device 10 in the forward direction indicated by arrow 40 in order to remove the grinding wheel 24 from contact with the tooth 26. This process is repeated until the tooth 26 is properly sharpened. When the sawyer is satisfied with the results, the device 10 is lifted up to remove the grinding wheel 24 from the gullet 33, and positioned in a similar manner under the subsequent tooth 26, which may be found in either direction (36 or 40).
Referring now to FIGS. 3a and 3b, a conventional front wear plate 30 is shown in various views. The front wear plate 30 is substantially rectangular in shape, and includes a set of legs 44 extending outwardly from one end thereof. The legs 44 extend downwardly as shown in FIG. 3a. Through a recessed aperture 37, the front wear plate 30 is affixed with a screw into a corresponding hole that has been bored into the bottom of the dividing block 16 (shown in FIG. 2). FIGS. 4a and 4b show the conventional back wear plate 32 which contains an angled portion 49 suited to fit around the bottom of the handle 14 (shown in FIG. 2). The back wear plate 32 contains a set of recessed apertures 52 that are used to attach the wear plate 32 to the bottom side of the handle 14 (shown in FIG. 2).
A problem with the prior art saw grinders, particularly with reference to the Jockey Grinder as described above, resides in the fact that the reciprocating forward and backward movement necessary to properly sharpen the saw causes the stationary wear plates to scrape against the top surface of the teeth. The friction resistance between the teeth and the wear plates must be overcome in order to move the saw grinder, and creates divots, grooves and other irregularities in the wear plates, often causing the teeth to momentarily “stick” into the wear plates. The irregularities created over time can be substantial, and increase the friction resistance that must be overcome to move the saw grinder. Having to overcome this friction resistance poses major problems for sawyers charged with properly positioning the grinder relative to the tooth to be ground. For instance, a sawyer or grinder operator must gently feather the grinder back and forth to effectively sharpen an individual tooth. This motion must be fluid. Any interruption in the sawyer's grinding motion raises the risk that a tooth will be chipped, cracked or weakened (“blued”) by unnecessary contact with the grinder wheel. Such problems are frequently encountered with the use of conventional saw grinders such as the Jockey Grinder, and lead to increased costs associated with the replacement of deformed wear plates and broken or weakened teeth. In addition, there is substantial down time associated with replacing damaged teeth, resulting in considerable production inefficiencies.
Accordingly there is a need for an improved saw grinding apparatus for allowing the saw grinder to easily move without having to overcome the friction resistance between the saw grinder wear plates and the peripheral edge of the saw blade. The present invention relates to improvements over the saw grinders described above, and to solutions to the problems raised or not solved thereby.